Modern wind energy installations are provided with rotors which have to be aligned with respect to the wind. Depending on the design of the rotor, it must be aligned such that it points into the wind (windward rotor) or away from the wind (leeward rotor), when seen along the rotor axis. In order to allow the rotor to be rotated to a correct azimuth position relative to the wind at any given time, a follow-up regulator with a weathervane is normally provided on the wind energy installation. This determines the direction of the incident wind and interacts with a pivoting device such that the rotor is pivoted to the correct azimuth position. The weathervane is generally mounted on a machine housing, at a point behind the rotor. It is therefore located in an area affected by vortices caused by the rotor. This results in measurement errors.
It is known from evident prior use for the discrepancies resulting from the arrangement of the weathervane behind the rotor to be determined and to be taken into account as a correction value. A calibration process must be carried out for this purpose during commissioning. One disadvantage of this method is that the calibration value determined in this way is applicable to only one rotor blade type and, strictly speaking, also to only one wind strength, at which the calibration was carried out. Furthermore, a further disadvantage is that the accuracy which can be achieved is not particularly good, even when using high-quality laser measurement methods. Normally, an accuracy of only 2° can be achieved. An accuracy such as this may appear to be acceptable since the efficiency of the wind energy installation varies only with the cosine of the position error. Discrepancies of up to 5° have been considered to be tolerable, against this background. However, it has been recognized that this approach has been adopted too readily, because further errors occur as well, because of unavoidable position errors with respect to the wind. Further causes of position errors include, in particular, the following:
Frequent or rapid changes in the wind direction, since the pivoting device cannot follow the wind without any deviation. Otherwise, this would easily result in overloading and premature failure of the mechanism. A further reason is the distortion of the air flow in the area of the weathervane, caused by the rotating rotor. This distortion is dependent on the wind strength and the wind direction and in general can be predicted only with difficulty. Inaccuracies also result from possible influences between adjacent wind energy installations. These are particularly pronounced when the wind energy installations are arranged in a line along the wind direction. All of these factors lead to a deterministic or stochastic position error of the weathervane. The errors that result from this cannot be compensated for completely by a simple, follow-up regulator for azimuth positioning. The position error results in detectable adverse effects, overall.
In order to counteract these adverse effects, optimization strategies have been developed. It is known from DE-A-199 34 415 for an improvement in simple follow-up control to be achieved by predetermining a plurality of power curves as a function of the wind speeds for power emission for various positions of the rotor with respect to the wind. These power curves are used to determine an optimum for calibration of the follow-up control, by means of optimization calculations that are known per se. The power curves must be determined and stored for various incidence angles during commission of the installation; it is also possible to adaptively vary the power curves during operation. One disadvantage of this technique is that the measurement of different power curves for different incidence conditions is complex.